This invention relates to a proportional electromagnetic-type direction-and throttle controlling valve.
Most conventional electromagnetic type flow, direction and pressure controlling valves employ the following devices for controlling the pilot pressure to control the spring centered main spool position.
1. Nozzle flapper type PA1 2. Pilot spool type
In a nozzle flapper type, high supply pressure is directly applied to the flow restricting orifice and the pressure down stream of the orifice is controlled by a nozzle flapper controlling nozzle flow. The pressure drop across the orifice is large compared with that of the present invention. Therefore orifice diameter for nozzle flapper restriction is required to be small which is disadvantageous as regards particulate contaminants in the system fluid.
In a pilot spool type, the pilot spool is apt to stick due to uneven pressure distribution around the spool. This is also caused by particulate contaminants in the system fluid.
The position of the main valve spool controlled by pilot fluid pressure controlled by a pilot spool is apt to drift according to fluctuation of the supplying fluid pressure.
Such proportional controlling valves require special equipment to protect the system from particulate contaminants of the system fluid and a high powered fluid supplying unit to avoid pressure fluctuation.
This equipment is usually cost high and needs careful maintenance.